Looks like some dry air might have punched into the northern eyewall again. Intensity might have leveled off or even weakened slightly. Sergio is definitely shaping up to be one of those systems who experiences several intensity fluxes. I think he might evolve into one of those storms who get caught up in ERCs and has trouble completing. Not saying he's going through an ERC right now though, no signs of that yet, I'm just making a guess as to Sergio's future.

Sergio might be making that run to Cat 4 now. Microwave showed a complete eyewall that was looking healthy and strong, the eye is clearing on satellite, and the CI# is now 6.3 with a center temp of +5.5C on ADT.

Looks to me like a secondary tropical cyclone has developed on the southwest side of Sergio in the outer bands.

3 likes

This post is not an official forecast and should not be used as such. It is just the opinion of MississippiWx and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution including storm2k.org. For Official Information please refer to the NHC and NWS products.

The above post and any post by Ntxw is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including Storm2k. For official information, please refer to NWS products.

Sergio's satellite presentation continues to look impressive thisafternoon. Several mesovortices can be identified rotating withinthe eye. However, the eye is somewhat obscured by upper-levelclouds and the eyewall edge is not clearly defined. Based on ablend of subjective Dvorak estimates from TAFB and SAB, the advisoryintensity estimate is held at 110 kt, which is the same as in theprevious advisory. Sergio should remain in quite favorableatmospheric and oceanic conditions for the next day or two, andadditional strengthening is expected through Thursday. ByFriday, Sergio will be moving over slightly cooler sea-surfacetemperatures and through a drier mid-level air mass, which shouldinitiate gradual weakening.

Sergio is currently heading toward the northwest, or 305/8 kt. ByFriday and Saturday, the storm is forecast to slow and turnwest-northwestward to westward while a mid-level ridge builds to thenorth and northwest of the hurricane. The official track forecastlies close to the equally weighted dynamical model consensus, TVCN.

It is of interest to note that a small disturbance currentlylocated a few hundred n mi to the west-southwest of Sergio isexpected to be drawn into the larger circulation of the hurricaneovernight.

Next advisory this should be the 9th Cat 4+ of the season. Very low shear ahead for a couple of days to peak.

5 likes

The above post and any post by Ntxw is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including Storm2k. For official information, please refer to NWS products.

The above post and any post by Ntxw is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including Storm2k. For official information, please refer to NWS products.

Sergio is quite the sight tonight over the eastern Pacific with alarge central dense overcast and mesovortices observed within thewell-defined eye. Subjective estimates from TAFB and SAB bothsupport a slightly higher initial wind speed of 115 kt on thisadvisory, which is a good compromise between lower microwaveestimates but higher ADT values. Notably, Sergio is the record most8th category 4 hurricane of the 2018 eastern Pacific season-breaking the old record of 7 set in 2015. Reliable records in theeastern Pacific for major hurricanes go back to 1971.

Further strengthening is possible during the next day or so whilethe shear is forecast to remain low and the water is quite warm.After that time, a combination of cooling waters and higher shearshould generally cause Sergio to weaken. This will probably be anunsteady process, however, since eyewall cycles are also likely overthe next few days. Overall, the hurricane should be on a weakeningtrend, and that is the NHC forecast, very similar to the previousone, and a bit higher than the model consensus.

Sergio is moving northwest or 315/8. This motion should graduallybend toward the west over the next day or two as the steering flowchanges from a ridge near Mexico to a building ridge to thenorthwest of the hurricane. Sergio could turn to the northwestearly next week as the hurricane comes under the influence ofa deepening trough over the far eastern Pacific and southwesternUnited States. The model guidance is in excellent agreement duringthe next few days, and no significant changes were required to theprevious forecast.

ERC? There's a moat-like feature on the NE sector of Sergio on AVN IR.

1 likes

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to RSMC, NHC and NWS products.

Sergio's intensity is estimated to have increased just a littlemore this morning, and it remains a powerful category 4 hurricane.Subjective Dvorak estimates are T6.5/127 kt from TAFB and T6.0/115kt from SAB, and the initial intensity is raised to 120 kt, whichis a blend of these numbers and very close to the latest objectiveADT estimate. Sergio's maximum winds are expected to change littleover the next 12-24 hours, and the hurricane's intensity could verywell be modulated by difficult-to-forecast internal processes suchas eyewall replacement cycles. After 48 hours, an increase inshear and gradually cooling sea surface temperatures should resultin some weakening, especially when Sergio moves more slowly at theend of the forecast period and possibly upwells some cooler waterfrom below. The updated NHC intensity forecast is nudged downwardduring the first 48 hours to follow the latest consensus aids, butno changes were made to the previous forecast beyond 48 hours.

The hurricane's initial motion is northwestward, or 320/7 kt, withSergio located along the southwestern periphery of a mid-levelridge extending westward from Mexico. This ridge is expected tobuild westward and connect to another mid-level ridge located nearthe central Pacific Ocean, forcing Sergio to turn westward, or evensouth of due west, between 36-72 hours. By days 4 and 5, a largetrough near the west coast of the United States should have greaterinfluence, causing Sergio to slow down and turn northward by theend of the forecast period. The track guidance is tightlyclustered for much of the forecast period, although a notablesouthward shift among the guidance, especially from the ECMWF,required a bit of a southward shift in the official forecast aswell.

Sergio remains a strong hurricane this morning, with subjectiveDvorak estimates range from 5.5 (102 kt) to 6.5 (127 kt). Whilesome slightly drier air has been ingested into the eyewall, cloudtop temperatures have cooled recently and Sergio appears poised toonce again close off this dry air channel. Based on these data, theinitial intensity is held at 120 kt. The intensity forecast ismostly a continuation of the previous advisory, but is slightlylower after 24 hours to reflect a blend of HCCA and other consensusaids. Vertical wind shear from GFS/SHIPS is forecast to remain at orbelow approximately 10 kt through 48 hours before increasing toabove 15 kt by Saturday. The primary limiter on Sergio's intensityappears to be SSTs which will drop off gradually, especially by theend of the forecast.

Sergio is continuing to move northwestward around the mid-levelridge which extends into the Pacific off of Mexico. The initialmotion is 320/8 kt. Objective track guidance is in fairly goodagreement on a gradual turn toward the west tonight and Friday inresponse to a second ridge which builds in from the west. Guidanceremains in decent agreement on Sergio then turning backnortheastward by the end of the forecast period as this ridge liftsnorthward and a highly-amplified mid-level trough digs into westernNorth America. The official track forecast is very similar to theprevious advisory through day 4 with a small shift eastwardthereafter to reflect a slightly earlier northeast turn in theguidance. This track philosophy is supported by essentially all ofthe ECMWF/GFS ensemble members as well.

The above post and any post by Ntxw is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including Storm2k. For official information, please refer to NWS products.

Sergio remains an impressive hurricane. Although the cloud patternis still symmetric and well organized, the eye has become ragged andcloud filled at times. The current satellite intensity estimatesrange from 102 to 127 kt, and the initial intensity is set to 115 ktbased on a blend of these data. The environmental conditions alongSergio's future path are expected to gradually become less favorableduring the next several days, with decreasing mid-level humidities,cooler SSTs, and a slight increase in wind shear. In response, allof the models show a gradual weakening trend through the period, andthe NHC forecast does as well. This forecast lies near the intensityconsensus aids and is largely an update of the previous one.

The hurricane is still moving to the northwest at 8 kt. A gradualturn to the left, or west, is expected during the next couple ofdays as a mid-level ridge builds to the north-northwest of Sergio.Late this weekend, a decrease in forward speed is expected as theridge retreats in response to a large trough over the southwesternUnited States. This change in the steering pattern should cause thecyclone to turn northeastward by the end of the forecast period. Theonly notable change in the track forecast is a sharper northward andnortheastward turn at days 4 and 5, to come in better agreement withthe latest consensus aids.